The present invention is in the field of non-invasive measurements of physiological parameters of patients, and relates to a device for measuring blood-related signals.
Numerous techniques have been developed for the non-invasive measurement of blood-related signals, being aimed at determining various blood-related parameters such as blood oxygen saturation and the concentration of substances contained in the blood, e.g., glucose. These techniques typically utilize a measurement device or probe, which is designed to be attached to a patient""s body (typically his finger), and includes an optical assembly for irradiating the finger with light and detecting its light response.
Most of the known devices are based on spectrometric techniques. According to these techniques, a tissue is irradiated with light of different wavelengths, and a photodetector detects light returned from the tissue. Analysis of the detected returned signal allows the determination of the required biological variable. The accuracy of the method depends on various conditions, some of which are associated with the detected signal and others with the irradiated tissue. This technique gives poor results due to a low signal-to-noise ratio, artifacts and the fact that the returned pulsatile signal might be very low.
Recently developed techniques propose various solutions directed towards overcoming the above drawbacks. U.S. Pat. No. 5,131,391 discloses a pulse oxymeter aimed at overcoming a problem associated with constriction of blood vessels that might occur during stress or invasive procedures such as surgery. To this end, the pulse oxymeter, in addition to a photodetector, has a warming device.
U.S. Pat. No. 5,638,818 discloses a measurement device having an improved optical probe designed so as to reduce noise in the course of measuring signals in a compressible tissue. The probe includes a base having an aperture for the finger to be inserted therein, which aperture leads to a chamber where a photodetector is placed in a manner to have no contact with the finger. A light source is affixed to the finger above the chamber. This design enables to maintain the optical path of transmitted light. A scattering medium is interposed between the light source and the finger so as to improve the signal-to-noise ratio. In a later patent of the same author (U.S. Pat. No. 5,782,757) a disposable optical probe and a reusable probe in the form of a padded clip-on bracket are disclosed. The probes are designed so as to fit comfortably onto a patient""s fingertip.
WO 9843096 discloses a measurement device, where measurements are applied to a part of the body whose thickness is modulated harmonically by at least two pressure modulating frequencies. This part of the body is irradiated with at least two different wavelengths, where at least one of them lies in a range of optical absorption of the blood components to be determined.
JP 10033512 discloses a measurement device having a slot for a patient""s finger to be inserted thereto. The walls of the slot are coated by an insulating material. A light source and a detector are accommodated at opposite sides of the slot so as to be at opposite sides of the finger.
DE 19629342 discloses a measurement device in the form of a holder for holding a patient""s finger at its one side in a manner to apply a slight pressure thereto. The device analyzes light reflected from the finger.
The above devices deal with natural pulsatile signals. What is actually measured by these devices is an enhanced optical pulsatile signal. It is known that a regular optical pulsatile signal is typically 2-3% of the total transmission. The above devices are capable of obtaining the enhanced pulsatile signal that reach 8-10% of the total light transmission intensity. This enhancement of the natural pulsatile signal is a boundary of all conventional techniques of the kind specified
A different technique is disclosed in a co-pending application PCT/IL 99/00331 assigned to the assignee of the present application, where the measured signals are not pulsatile. According to this technique, a state of blood cessation is created in a medium under measurement. This enables to significantly enhance the measured light response of the medium, as compared to that of the previously described techniques dealing with the pulsatile signals.
There is accordingly a need in the art to facilitate non-invasive measurement of significantly enhanced blood-related non-pulsatile signals, by providing a novel optical measurement device.
It is a major feature of the present invention to provide such a device that can be easily attached to the patient""s organ and enable to create the blood cessation state within a measurement region.
The present invention takes advantage of the fact that measurements taken during the state of blood cessation allows for a significant increase of the blood-related signals, as compared to those taken during the state of normal blood flow. This concept is disclosed in a co-pending application PCT/IL 99/00331, assigned to the assignee of the present application. To create a state of blood cessation within a patient""s organ, over-systolic pressure should be applied thereto. Measurements are taken at a location downstream of that where the over-systolic pressure was applied with respect to the direction of normal blood flow.
The main idea of the present invention is based on the fact that heating and optionally pressuring, effects significantly enhance the blood-related signals to be measured. The measurement device according to the invention includes a measurement unit and occlusion assembly, which are spaced-apart from each other along the patient""s organ, and the measurement unit comprises a substantially flexible heating element. This element, on the one hand, enables to heat an area under measurements to a desired temperature, and, on the other hand, is capable of providing pressurization and comfortable fixation of the organ, and prevents its displacement relative to an illumination-detection assembly during measurement.
There is thus provided according to one aspect of the invention, an optical measurement device for attaching to the patient""s body to perform non-invasive measurement of blood-related signals, the device comprising:
a measurement unit for attaching to the patient""s extreme organ, the measurement unit comprising an illumination-detection assembly for illuminating a first region within said organ, detecting light response of the illuminated region and generating data representative thereof, wherein the measurement unit comprises a substantially flexible heating element engaging at least a part of said first region for heating it to a desired temperature;
an occlusion assembly for applying substantially over-systolic pressure to a second region on the patient""s body located upstream of said first region with respect to a normal blood flow direction; and
a control unit, which is coupled to the measurement unit for selectively actuating the measurements, analyzing data indicative of the detected light response and determining at least one desired parameter of the patient""s blood, and is coupled to the occlusion assembly for selectively operating this assembly.
The occlusion assembly includes a cuff associated with a pneumatic drive for applying the over-systolic pressure. The cuff is either a ring mountable onto the patient""s organ, or a band with Velcro-like fasteners.
The measurement unit may be in the form of a clip supporting the illumination-detection assembly and having the substantially flexible heating element attached to its inner surface. Alternatively, the measurement unit may comprise only this substantially flexible heating element that supports the illumination-detection assembly. To this end, the element is in the form of a cuff-like cushion to be wrapped around the organ within the region under measurements. This cuff-like cushion is associated with a pneumatic drive, constituting together a pressurizing assembly for supplying desired, substantially under-systolic (e.g., 10-50 mmHg) pressure. His pressurizing assembly is aimed at, on the one hand, adjusting the cuff-like cushion to a specific patient, and, on tie other hand, providing slightly pressurization of the patient""s organ within the measurement area, thereby enhancing the measured signals.
Preferably, the desired temperature for heating the region under measurements is approximately 37xc2x0-38xc2x0. Heating can be either continuously or by applying short thermal pulses (e.g., electrical or light energy) to accelerate heating of the measurement region to the desired temperature.
The substantially flexible heating element may be in the form of a film made of a thermoconductive material, or of a non-conductive flexible material with a heater implemented therein. Alternatively, the substantially flexible heating element may be a two- or three-layer structure. If the two-layer structure is used, the first layer, which is in contact with the patient""s organ, is made of an insulating, material, and the second layer is made of an electrically conductive (i.e., heating) material. If the three-layer structure is used, the first layer, which is in contact with the patient""s organ, is made of an insulating material, the intermediate layer is made of a heating material, and the third layer is made of a dielectric material.
The illumination-detection assembly may be of any known kind. The assembly may be designed for detecting either light transmitted through the illuminated region or light scattered (reflected) therefrom.
Preferably, the patient""s organ under measurements is his finger.
According to another aspect of the present invention, there is provided a finger holder to be used in a measurement device performing non-invasive measurement of blood-related signals, the finger holder comprising:
a measurement unit for attaching to the patient""s extreme organ, the measurement unit comprising an illumination-detection assembly for illuminating a first region within said organ, detecting light response of the illuminated region and generating data representative thereof, wherein the measurement unit comprises a substantially flexible heating element engaging at least a part of said first region for heating it to a desired temperature;
an occlusion assembly for applying substantially over-systolic pressure to a second region on the patient""s body located upstream of said first region with respect to a normal blood flow direction; and
a control unit, which is coupled to the measurement unit for selectively actuating the measurements, analyzing data indicative of the detected light response and determining at least one desired parameter of the patient""s blood, and is coupled to the occlusion assembly for selective operating this assembly